1. Field of the Invention
The present invention relates to a photographic printer and more particularly, to a photographic printer in which an image recorded on a film is photometrically measured by light emitted from a light source and the light is transmitted through a light controlling filter and the film, and thereafter, the image recorded on the film is printed onto a photosensitive material by irradiating the light, which was transmitted through the light controlling filter and the film, onto the photosensitive material.
2. Description of the Related Art
In a conventional photographic printer, before an image recorded on a film is printed on a photosensitive material, light emitted from a light source and transmitted through a film is separated into red, green and blue through photometric filters, and is received by optical sensor to measure (photometrically measure) the amount of the transmitted light of each color. Exposure control techniques, in which exposing conditions for printing the photosensitive material for each color are computed based upon the measured data, have been known.
Further, in recent years, photographic printers equipped with photometric means have generally been used for obtaining exact printing exposure conditions In accordance with the subject matter of images. In such printers, an image recorded on a film is divided into a number of pixels and each of the pixels is separated into red, green and blue colors and photometrically measured by the photometric means. The above photometric means can be realized by using a CCD as a light detecting sensor and a gelatin filter (i.e., filter manufactured by sandwiching, between a pair of glass plates, a gelatin layer which absorbs aqueous solution containing a mixture of several tens of organic dyestuffs) as a photometric filter.
A light source installed in a photographic printer requires some time to recover illuminance of light emitted from the light source when light emission is restarted after having been once stopped. Therefore, emission of light is continued while printing exposure is not carried out so enable restarting in a short time after printing exposure is temporarily stopped. Accordingly, the light controlling filter, the CCD and the gelatin filter are always irradiated by light. In general, the light controlling filter formed by a metal deposited filter is not prone to fading, and therefore, there is no concern that the filter will deteriorate even if the filter is irradiated all the time. In contrast, the gelatin filter tends to fade when strong light is irradiated thereto for a long period of time. A drawback arises in that such fading promotes deterioration in the performance of the gelatin filter. Further, the light detecting sensor such as a CCD causes sticking and the like, and has a drawback in that the function thereof deteriorates when strong light Is irradiated thereto for a long time.